Convection inclinometer



Dec. 9, 1952 R H, VARI'AN 2,620,571

CONVECTION INCLINOMETER Filed June 20, 1945 4 Sheets-Sheet 2 CURRENT INVENTOR RUSSELL f/.lqR/,Q/V Y( lDc. 9, 19.52 R, H, vARlAN 2,620,571

CONVECTION INCLINOMETER Filed June 20, 1945 4 Sheets-Sheet 3 INVENTOR Passau A. )QW/,4N

. 9, 1952 R. H. vARlAN coNvEcTIoN INCLI'NOMETER Filed June 20, 1945 4 Sheets-Sheet 4 INVENTOR Russa/ 1 H. l/R/A/v Patented ec. 9, 1495.2

UNITED STATES PATENT OFFICE CONVECTION INCLINOMETER Russell H. Varian, Garden City, N. Y., assignor to The Sperry Corporation, a corporation of Dela- Ware 4 Claims.

This invention relates to improvements in inclinometers and to the adaptation of such devices as convection, gravity-determining elements in cooperation with gyro erector systems.

Hitherto, inclinometers, such as used in aircraft, have required the use of suspended weights or pendulums to determine the normal vertical. Such pendulums were set up in aircraft under c-onditions permitting the determination or establishment of the position or attitude of the aircraft with respect to the vertical. Owing to the mass of the pendulums, a great deal of trouble is encountered in operation, particularly when aircraft, such as an airplane, is subject to rapid changes in velocity, course and attitude. The swinging of the pendulum, due to such changes, introduces transients in the operating system which would destroy stability of operation. To avoid this difficulty, means, usually automatic, are sometimes provided to disengage the pendulum from control during such periods. Even where gyro verticals are used as base lines for aircraft it is usual to employ some type of pendulum or level for controlling the gyro vertical and hence although the gyro vertical integrates the errors of the pendulum, persistent errors will cause deviation of the gyro vertical.

It has now been found that the difiiculties above enumerated may be considerably reduced or eliminated by my improved device in which a rising column of liquid is utilized to determine the normal vertical, and special thermoelectric and photoelectric circuits, as well asY impedancecontrolled circuits, are used to determiner and utilize the orientation of the normally vertical, moving column, as its surrounding fluid and container vary in orientation to agree with positional variations of the aircraft in whichthey are incorporated. The use of convection, gravity direction-determining devices avoids, to a considerable extent, the difliculties inherent in pendulous devices and inclinometers and introduces novel operational features. My invention utilizes an inherent differential in refractivity of Athe fluid used, due to the temperature differentialbetween the rising column of heated fluid andthe cooler body portion thereof. The rising column isV visible to an observer. Also, thermoelectric currents can be generated by the action fof thelmoving column on suitably oriented thermocouple's.-

A Wheatstone bridge vconnection may be utilized to control appropriate servomotors or torquers with the advantage that the former may be supplied with sufficient power through anamplifer to operate a control surface of an aircraft, if desired. Such direct-powered resistance-controlled circuits are not only of sufciently high voltage to be'suited for direct operation of controlled elements, but the circuits controlled may be located at a distance from the pick-off element proper.

For the direct control of appropriate servomotors or torquers, the inclinometer herein may be incoporated in a photoelectric control system for the motor or torque control circuits, supplied with sufficient power to operate same. My inclinometer is adapted for use as a gravitational reference to control a gyro vertical for which use it has many advantages over pendulums suspended on the 'gyroscopa as has previously been the practise. According to my invention, my improved thermal reference may be mounted independently of the gyro and its position compared with that of the gyro by photoelectric or other means not requiring contacts or slip rings to be used on the gyroscope.

It is an object, therefore, of the present invention to provide novel convection, gravity direction-determining devices utilizing the differential refractive and thermal aspects of a moving column of fluid in a bath of the same iiuid.

Another object of this invention is the provision of visual means for determining the angle of inclination of the moving cone, column, or pencil of fluid from both the horizontal and the vertical.

Another object of this invention is the provision of photoelectricv means for determing the angle of inclination of the moving cone, column, or pencil of fluid from both the horizontal and the vertical and extraneously powered gyro erector means controlled by the photoelectric means.

A further object of the invention is the provision of special non-pendulous gyro erectors controlled by convection, gravity inclinometers, through the intermediacy of apparatus energized by differential thermoelectric, as Well as resistance-controlled and photoelectric-controlled currents.

These and other desirable features of novelty and advantage of the present invention will be described in the specification, certain preferred forms being illustrated in the drawings byl way of example only, for, since the underlying principles may be embodied in other specific installations, it is not intended to be limited to the ones here shown, except as such limitations are clearly imposed by the appended claims.

In the drawings, like numerals refer to similar parts throughout the several views, of which Fig. 1 is an elevation of a bidirectional in- 3 clinometer embodying the principles of the present invention;

Fig. 2 is a horizontal section taken on line 2-2 of Fig. 3;

Fig. 3 is a vertical section of the structure shown in Fig. 1;

Fig. 4 is a View similar to Fig. 3 showing electrical connections for determining orientation of the device;

Fig. 5 is a vertical section through the device of Fig. l showing the arrangement of a thermoelectric pick-off means;

Fig. 6 is a plan view of the thermoelectric pickoff means used in Fig. 5;

Fig. '7 shows top and bottom views of a modified thermoelectric pick-off means using special heat collector grids;

Fig. 8 is a graph illustrating the electrical characteristics of the grid of Fig. '7

Fig. 9 is a schematic illustration of a wiring diagram including the thermoelectric pick-off of Figs. 5,V 6 and '7 coupled to a gyro erector circuit;

Fig. 10is a View similar to Fig. 6 showing a directly powered pick-off construction utilizing resistance controls having negative, thermal characteristics;

Fig. 11 is a Wiring diagram of the resistance pick-off ofA Fig. 10 with Wheatstone bridge couplings;

Fig. 12 is a wiring diagram of thevresistance pick-off of Fig. l0 and Wheatstone bridge connections to output transformers;

Fig. 13 is4 an elevation and Fig. 14 is a top plan of a gyro erection control system incorporating the inclinometer herein with a photo-electric pick-off means; and

Figs.- 15 and` 16 are face views of the photoelectric cell showing the reference shadows on the cathodes in vertical and tilted positions, respectively.

Considering the invention generally, the primaryor basic form of` the inclinometer herein functions .as a rising vertical column of fluid, which risingcolumn establishes a reference by visible or electric means.

A wide variety of uids maybe used in the inclinometers of the present invention. They shouldhave an adequate temperature range be tween the freezing and boiling or ash points and should not at anytime become too viscous. Turbulence ofthe iiuid ,within the envelope should be kept to a minimum or should besubstantially eliminated so that thedevice will not provide an erroneous indication. Elimination of` turbulence inthe fluid is especially important where visual indications are to be used. Additionally the fluid should have a high coeiiicient of lexpansionaccompanied by a noticeable' change in the index of refraction when its Vtemperature is varied. Transformer cil having a viscosity of 10 centi- Stokes at 100 C. has been Vfound satisfactory. Also,` other oils may be used. Thesilicone fluids bient body thereof, while the descending column or organo-silicon products show a low'rate of viscosity *change with temperature, and Vthis stability of viscosity makes them suitable for airplane instruments whichmay undergo great temperature changes in a single flight. yThe'viscosity of the high-viscosity ltype silicones may vary from 100 to 1,000 centi'stokes. The ash points range from 600 F. to 640. F., whichfis considerably higher than that `of hydrocarbon oils of equal viscosities at roomtemperature. The low viscosity type silicones have viscosities ranging from .65to 100 centistokes. These fluids have boiling points ranging 'from 99.5 C. .for the .65 viscosity to of cooledoil is colder than the body thereof, whereby the refractive index of the moving column is sufciently different to afford visual identification thereof against the body of the fluid. In the case Where thermoelectric or thermoresponsive electric resistance pick-offs are used, the heated o r cooled column impinging on specially oriented and connected thermocouples or thermally responsive resistance elements will differentially heat or cool the Various thermocouples ,or resistance elements, thus giving rise to thermoelectric currents of varying intensity or control currents varied in accordance with the thermal response of the resistors. To utilize these rela-- tively weak thermoelectric currents, they are fed through a vibrator or interrupter circuit to the input of a torquer control, including a first amplier stage of an electronic and amplifier cir'- cuit. As such amplifying circuits are well known per se, they Will not be described in great detail herein, except in connection with the specific means of feeding signals thereto corresponding to the variable orientation of the reference column of heated uid. Where A. C. powered resistancecontrolled Wheatstone bridge circuits are used, they may use high voltage and directly control the servomotors or other control devices without the `necessity of signal amplifying means.

The invention herein will now be considered with more specific reference to the devices shown in the drawings in which the principles are embodied.. In the form shown in Figs. 1 to 3, a casing or envelope I0 is shown as a generally cubical container having translucent or transparent front and back Walls Il, I3 and side walls I5, II, together with bottom I9 and a top 2|. The Walls I I -and .I5 may comprise translucent panels 23, 25 of frostedglass, or thel like, preferably provided with scales 21, `2s calibrated to indicate the angular` deviation of the container or inclinorneter from the vertical.

TheY chamber IIJ is provided With an expansible overflow chamber 3| adapted to accommodate the overow, onexpansion, of fluid 33 contained in the chamber. Centrally of the base I9 there is provided a conical heating surface 35m/which is preferably pointed, as shown, to tlfierebyv provide a substantially point-source `of heat. This heatingA surface is heated by heating element 3'1 contained therein and supported on a bracket 39 secured to base I9. An insulating bushing 4I servesV to hold the base 'of the heating element 31 Vand permit introduction of the feed wires 43.V The inclinometer l0 may be mounted on a bracket 45 having arms` 41, 49 to which the chamberA is secured as by meansof boltsor screws 5I. Inits simplest form Vof operation, {When the heatingfelement 3'Iis energized, .corneal heating surface 35 heats the circumambient oil and the latter rises in a. restricted vertical column or pencil 5'3 within the body of the liquid 33. Due to theV difference in the'index of refraction of theheatedcolumn as compared againstvthe backgroundof the cooler', bodyl of liquid, theposition ofrcolumn 53can be readily established or observed.

Whilerthe liquid in the inclinometerfhasbeen described asbeing-locally heated to establish a rising column of differentially heated fluid, which incidentally also. warms the entire body of -the liquid suiiciently to keep its viscosity low it will,r of course. be understood that the inverse phenomenon offcoolingmay be utilized. Under such, circumstances, a` cold Aspot orcooling arrangement may be` applied orused'at the upper surface-or top of the inclinometer-to establish a descending cool column of reference liquid move ing. in a bath or body of circumambient warmer iluid. Wherefa. cooled column is used, and electric pick-oils are4 included in thegsystem, the pick-oils will .desirablyfy be. mounted at they bottom of the inclinometer.

To enable the inclinometer to be used on.-v an aircraft, orthe like, in association with the in strument board orpanel, means are provided to illuminate thefbodyof. iiuid so as topermit the;y visual identification of the position oflthe movingcolumn of. iiuid 53. For this purpose pointV source lamps 55, 51. are mounted in housings-59, 6I at adjacent sides of :the casingl and opposite thepanels 23, 25., The housings 59, II arerformed as paraboloids of revolution, and the convection Y current vwilli appear as a sharp line v.regardless of Whether v it, vis fex'actly vertical inthe chamber, or whetherit is inclinedatfan angle thereto. The lamps may be mounted in the usual sockets63, secured onto bases; 65 of thehousings and spaced awayfrom thepanels asuicient distance. to. avoid or -precludeany direct heating effects Vonthe-bodyof uid'33.

The, front or.4 main panel 23: with= its in clinometer scale V 21; can. be read directly by the pilot,. who .can determinethe amount. ofl angular inclination fromv the vertica1y by visual. inspec-Y tion. To determine they amount ,and .direction of pitch inclination, thejside panel 25; with-its inverted; scale 29 is viewed in aslantrnirror 51 secured-tothe casing. I0 byabracket 8.; as shownmoreparticularlyinFigs. 1 and 2.; From this showing, it will; be yseen that;l the pilot; can visually' determine atea -singleglance bot-h the ioreeand-,aft and -`lateral attitudescf; his.; ship. The. chamber as a `.WholeisY alwaysv radiating heat, so ,the .-risingcolumn is ,always .hotter, than the rest-ofthe oil, and thedevice can-y operate continuously.

Whilefthe body of -.liguid 33 may besubjected to mass. or acceleration effects -arisingffrom the operation of anyV aircraft, it will benoted that this v.body of.- liquid, is restricted orwholly coniined, in a closed containenand is thereby precluded; fr omexhibiting or,y being subject to turbulence or surging.V The .device isvery Aresponsive `due .to the maintenanceofthe fluid. in a ,mobile or nonviscouscondition.

Theform-shown in Figs. 1 to.3 may. bemounted in; a,- cockpit, at V about eyeflevel, and to either side of the; pilot. Where vthe device isto be in stalled,; say,v at` ytherrighthand side of fthe. cock pitfthe mirror. 61 wouldbe shiftedfover to co-` operate .vvithvpanelv I1 while the lamp` 55 and housing 59.1vil1 :be shifted to cooperatey with panel 5 'I The, device .just described is essentially. avisual indicator. In ,the formshown. in..F ig. 4, the

inclinometer. may. be. provided, Witha..Y dial-indicatingmeans w1 I. includedin `or -rorming -a part of .an- ,ampliiier 13;. In. thisform, opposed thermometers 15,. 18; may ,be `mounted. in.,A the cover 2I andconnectedthrough lines-,19, BI to.

indicator 1I Desirably, thethermometers 15, 18 may comprise calibrated thermocouples.. It is to beunderstood, of course, that in the forms ofthe invention in which `electrical, signalsnerating means or signal producing meansy are provided, thefluid container orenvelopelmay be; cylindrical in shape or of any; otherv desiredmum temperature ranges, means are provided to automatically control the temperaturethere-f of. The feed lines 43 to kthe heater 31 vinclude a switchV 33v serviced by current input 85=which may supply an alternatingcurrent of. suitable voltage.v A` second heater or grid,` 8Dl may/'ba mounted in the bottom of the device and connected to service lines through leads 82v and thermoswitch 84. Aqthermostatl is mounted in the cover and willv be-connectedto the there moswitch, in any suitable manner, as through lines 89. By suitably calibratingthe thermostat and thethermoswitch, the bodyf of liquid. 33 .can beraised to or maintainedatany de siredLOD: erating; temperature, w lr1,i c h1will usually-*be apr precably below, that ofthe reference stream 53, This feature is of particular-. importanceif;the inclinometers are to be fabricated andstocked for distribution to various parts-ofthcwlld.

In the tropics it will be obviousthat thelbody of lfluid V33 would not need any .g extraneous :heat However, in -the arctic or inqhigh altitude flying-,- the fluid 33 might well require positiv@-l heating to enable it to function as desired. The., thermostat ycontrol ofthe heater, vmakesthe Vsystem trulyy flexible and adaptablefor a1l: fiying;con; ditions,

Where the inclinometer described` abovejs to be fused as a-yro erector, an electrical pick;- ofi'v may be incorporated therein.v One. formfof suona system isillustrated inFigs. 5, 6, and- 9, and willnow be described, In this. system the usual container .lil is provided, with the heating elment '35 and accessories-but the wallsneed not be translucent or transparent. In this. system avtherrnoelectric pick-off 93'iis provided, which pick-off comprises a triangular member vizfof constantam, German silver, or.v suitable metal, having `apexes 91, SI1-and IUI. Leadgwires- I03, |05 and I01- of different metal are Welded tO, the sides orthe triangle, -as indicated at; I 09, I I Ia Land II3. TheleadsV I3, |05; and I 01 aretaken out through apertures H5;` II 1 and I Iainthe walls of the container, the aperturesbeing :suitably scaled, as shown.` Toincreasethe. thermo;ieie cency of thethermocouple system, rods .l 2 Ii are weicedkor braced, as indicated at lzatotheleads 33.495A and |01-V A. sufficient; number orthese rods orlradiators are'fsecured in place on-the leads and are arranged ini parallel and without interconnection to, the several leads, so thateach leadfhas; its own separate, heat-collectinggrid structure.. With this arrangement, av maximum amount, of heat is Acollected uat eachmainrthermojunction |09, IILand. II3.

In ,-normal, verticalcondition of :thel gyro'y er'ector,fthe risingv column or pencil 53- of heatedifluid will impinge at. the geometric center I 25 -v of :the

thermocouple: system, and;l each leg.v oiA the deltay 7 connection will be uniformly heated. Theresult is that all three junctions willbe at the same temperature, and no current will flow. When the container or chamber 9 is tilted from its normal vertical position, the column 53 will apparently be tilted 4in the opposite direction. With such angular variation, the heating effect of -the column will be shifted from the center of the grid system IE5-to any one of thethree grid -systems associated with leads |53, |55 and IOL-or combinations, in varying degrees of`in tensity. This will result in the diierential heating 'of thermocouple junctions |59, Hi andr'Hit. When the currents generated at these respective junctions are drawn on through their respective leads, an amplied signal may be fed into appropriate servomotor controls on aircraft. To perfect this result, the system indicated in Fig. 9 may be used. A Y-Y connected stepup transformer |21 is provided with primary windings v |29, |3| and |33. These windings are interconnected to a common return and are individually connected through make-and-break keys |31, |39 and |4| to leads |55, |53 and |51, 'respectively. The make and break keys are caused to vibrate by means of coils |43 simultaneously fed with pulsating current from a source of pulsation current |45. With the source of pulsation current in operation, the make-andbreak keys will be simultaneously operated and the thermoelectric currents developed in device 93 will be fed into primaries |29, |3| and |33 as interrupted D. C. To step up these currents, secondaries |41, |49 and I5! are connected through a common line |53 and individually led to lines |55, |51 and |59 to the control grids of amplifier tubes I6 |53 and |55 of a rst amplification stage of any suitable gyro erector or torquer control circuit.

rAs shown in Fig. 9 a torquer |05 comprises a A wound stator having windings |54, |05 and |08 joined at mode or junction points HG, ||2, ||4, as shown. The junction points are connected by leads 94, 95, 98 to the plates ll, |53, |65 of the amplifier. The rotor coil |82 of the tcrquer is connected through leads |46 to the source of pulsation current |45, previously described. While the one stage of amplification has been indicated it will, of course, be understood that this showing is essentially diagrammatic and the invention contemplates the use of any desired number of stages of amplification.

It will be seen that with the differential heating of the several junctions of thermoelectric device 93, one junction may receive more heat than the other and will, therefore, serve as the hot junction, while one or both of the other junctions may serve as the cold junction. Additionally, two junctions may be uniformly heated and a. third junction served as the common cold junction. Under these conditions, the energy fed into the transformers will vary from maximum to null and any two signals may be cancelled or modified so that the input into the amplifier system may comprise a definite, oriented signal which can be moded, plus or minus, by the signal or signals from the associated legs of the thermo battery 53.

In Fig. 7 there is shown a novel pick-ofi structure showing superimposed semicylndrical cellular or honeycomb collectors or grids 60 and 50 having a peripheral sheathing 62 of suitable metal, thermally responsive resistors or thermoelectric generators 64 being brazed or otherwise secured to the surface 62 in good heat conductive relation. The elements 64 will be provided with suite able current leads 55, which may be connected in the erecting circuit as shown in Figs. 9, ll'and 12. In the showing of Fig. '7, two pairs of units E0, 50 are mounted in quadrantal relation, with each pair rotated through an angle of with respect to the other pair and a gap Vor space 68 formed between the elements of each pair. This particular construction will give an operational characteristic illustrated by the curve of Fig. 8 when two halves of a unit are tilted out Ofthe vertical plane Y(at right angles to the drawing). The righthand segment, assumed to be in the path of the convection column 53, will provide the hot junction Vof a thermocouple, at junction 65a, and the left hand segment will provide the cold junction at 56h. When the convection` stream is in this position the current will be owing in one direction and is represented .by 65a, Fig. 8. When the convection stream impinges on the ileft hand segment, the current is reversed, and is represented by 50h in Fig. 8. -In the apparatus shown inV Fig. 7, the grid segments including'the'grid mesh 60 and 5B' and the outer grid ring i62'and the leads B6 would preferably be made of copper, while the element 64 would be made of constanten, or other suitable metal. If desired, the thermocouple wire |34 could be duplicated on each pair of grids and connected in parallel to equalize the signal for different positions of the convection stream on one of the grids. In the gaps 68 between the elements, no current is generated, and the voltage curve will have a relatively sharp differential indicated by the slope 68a in the curve of Fig. 8. The cell or heat-responsive structure of members 6B may be made of any suitable height to increase the active area thereof. The particular cell structure may be prepared by :the longitudinal or axial splitting of grid structuresprepared according to the teachings of application Serial No. 588,589, filed April 16, 1945 by. `the present inventor and Sigurd F. Varian.

Referring now to Figs. 10, 11 and 12, invention herein is illustrated with reference to the use of Wheatstone bridge circuits which are adapted to directly control servo mechanisms or' indicators. For this purpose, a special pick-off 200 is'used. This device comprises an assembly of resistance elementsl mounted'in a Y or star connection in a suitable container. l The contain'erlz 02 fmay be four-Walled, as shown, and is apertured to receive leads 204, 256 and 208 of the .pick-off 'connected at center or midpoint 2|0. Special resistance elements 2 I2 are electrically connected to the leads and in series therewith.

The preferred type of resistance element is the so-called Thermiston which is a special metal in which the change of resistance with current or voltage varies rapidly with the change of temperature. Almost-always, the resistance of these elements decreases with temperature increase, and hence they areV characterized by a negative temperature coeilicient. At constant temperature, they follow .Ohms Law. `These'. resistance elements may be made of semi-conductors com prised of materials such as uranium oxide (UsOa) nickel oxide (NiO) and manganese oxide y(MnzOs). The uranium oxide has a specic resistance of 50,000 ohm/cm. at O degrees centigrade, which decreases rapidly with rise in temperature, being 2,800 ohm/cm. at degrees and 15 ohm/cm. at 500 degrees centigrade. A mixture of nickel oxide and; manganese oxide exhibits a still larger negative temperatureco'eflicient of resistance, the specific resistance values'at 0 and 500 degrees centi- 'grade being --respectively .-10,000 and 0.8 ohm/cm. The current passed through these elements varies quickly with changes of temperature so that there is little time lag involved.

The several Aresistance elements or Thermistors are in heat conductive relation to a plurality of 'concentric rods or `wires 214, 216, 218, 220 and 222 Yforming a heat-collecting grid. These grid members are not in electrical contact with the leads 204, 206, 208, or any-of the resistance elements 2 I2. A power lead 224 is connected to the apex 210 of the pick-off grid. The -grid is `heated in the same manner as that shownin Figs. 5 and 6.

vTo utilize the resistance modied differential currents set up in the various branches of the pick-off, the circuit indicated ,in'Figs 1l and 12 can be used. A'pair of Vleads 224, 226 is 'connected to a source of alternating current and to the three-legged pick-off, `just described, and a cooperating three-legged Wheatstone bridge. In the schematic diagram of Fig. 11,'the Wheatstone .bridgehas t'nreelegs 228, 230 and 232 and a common junction 234. Leg 228 is joined to leg204 of 'the pick-off at 236, while legs 230 and 206 have a common junction at 238, and legs 208 and .230 have their junction at 240. Primary coils 242, 244 and 246 of transformers-248, 250 and 252 (Fig. 12 are bridged across the junctions 236-238, 23S-240, and 240--236, respectively, serving as Crossovers in the Wheatstone bridge circuits. `The secondaries 242A, A244A and 246A are connected to control circuits as desired. While these pick-offs have been shown as inductive, the invention contemplates the use of other couplings, including capacitative and resistance couplings. In Fig. 12, the various junction points are shown connected by leads, but the arrangementis essentially one of direct coupling, as indicated in Fig. ll. For purposes of convenience, these leads, representing a common junction point, vhave been Y-identied with their reference numbers.

'With 'the circuit arrangements showin-it will be appreciated that the Wheatstone bridge and associated transformer sections may be'separately mounted from the pick-oir element proper and interconnection made by suitable wiring.

In operation, with pick-ofi' l260 in neutral position, and all parts uniformly heated, the legs of the bridges will be at uniform potential. Whenever the heating'eiiect varies in any sector, differential currents willbe delivered from the legs ofthe pick-off to the appropriately selected legs of the Wheatstone bridge, and the crossover transformers will deliver variable currents to the system tofbe controlled. The speciflc control mechanism utilizing the differential currents developed in the novel pick-oif-Wheatstone bridge arrangement is already known in :prior patents and `applications and Will not be described herein in detail.

Referring now to Figs. 13 and 14, these show how 'my invention may be applied as a gravitational controller for gyro vertical. In these gures there is shown an optical typeof convec- 'tion-erector in which the inclinometer or convec tion part of the erector together with al1 the electrical circuit parts and controls is fixed to a case, and the gyroscope which is to be controlled carries only a cylindrical rod or tube whichintercepts two vertically displaced horizontal :beams of light. `Under level flying conditionsthe beams of light will be intercepted by the rod or cylinder mounted on the gyroscopeand a 'shadow will ygimbal 304 having bearings 31.16. gyro rotor 300 Ais mounted a cylindrical post or 10 be cast behind the intercepting member. Within the shadow of this interceptor will be mountved a photoelectric cell havinga common grid and vertically spaced oathodes connected to an amplifier circuit which controls a torque motor mounted on .the .gyroscope casing or gimbals. The torque motor is powered by a generator driven with a shutter which interceptsa focused beam of light from a suitable light source and .directed onto the'inclinometer or convection device, so that `its beam is 'Varied or displaced by the transient relation of the vertical column or cone of heated or cooled fluid'set up in the inrclinometer.

Considering this controlsystem in specific detail, an attitude gyro orgyrovertical 300 is supported `in bearings :302 which .are Vmounted on On top of the tube 308. This member'may or may not rotate with the rotor, depending on 'the design of `the rotor bearings` The optical system V'adapted 'Sto .cooperate with the rotor Yindex or columns303comprises a source of light .310, allens'312, shutter 1314, with inclilnometer 316, and convection stream 318. The

sides of the .container 316 vare provided with parallel transparent lwindows 320, 322 vtransversely of the 'beam of light 4from 'the lens. lA pair of glass plates 324, T326 are set up on ends and set one upon the other in v90" relationship, as shown lmore particularly in Fig. 14. Photoelectric -cell i300 -is -mounted "in the normal path of the beam lof light passing through'the incli- 'nometer and the oblique plates. 'This member one terminal of a suitable battery 4and terminal 346 connectedto the end of the anode screen 334 `may serve 'as the other connection to the B-'battery. `'2i-he cathode 336 is ldirectly connected throughiline 352 to'an amplierr3'50 land cathode 338 is connected'to the amplifier 350 through'line 354 and variable 'resistance 342. A torque vmotor 360 is connected to the amplifier through lines 362 and also through lines 364 to'generator 366 mounted on shaft "369 of motor 310 which drivessnutter 314. The -shaft 369 may be mountedvin a bearing 312 securedto'or formed as part 'of a supporting bracket 314.l AThe shutter y3 1'4 will be provided with `suitable radial aperand form a parallel beam 313.

tures 315.

The light from -source l310 will fall on'lens312 The beam -313 will pass through the'cell 316. That portion-of the beam which cuts reference column 318 ofthe inclinometer will .be re'fracted-and cast a shadow indicated generally by the numeral 319. This shadow or'beam -313 will impinge on the angularly displaced refractive -plates 324 and 326 where it issplit'to give an upper shadowf325 and a lower shadow .321 vwhich are-laterally displaced or widened as indicated in Fig. 14.

The combined width of the offset shadows 325 and 321 will desirably exceed :the diameter of rod or tube 308 and of the shadow 300`cast thereby. Referring, in this respect to the details shown in Figs. l5 and 16, it will beinotedthat 'the shadow 309 is vertically'centered in kthe iace of photoelectric cell 330 fand is alternately `overlapped a'tthe sides by shadows 325 and .321 Vre spectively. It will be noted further that shadows 325 `and 321 are vertically offset with respect to each other. The shadows as combined in Fig. 15 will mask substantially equal areas of the photoelectric elements or cathodes 336 and 333. Under these conditions balanced currents obtain in the leads 352 and 354 which feed amplifier 350, and no error signal will be developed.

Under the conditions shown in Fig. 16 the reference member 308 is tilted to one side. The lower photoelectric element or cathode 338 will be seen to be masked by the combined shadows 309 and 321. The upper cathode 336 will have the shadows 325 and 309 substantially coinciding so that its active or exposed area is increased by at least half the width of the shadow 309, while the lower element 338 has had its active area decreased by substantially the same amount. This gives a, relatively great increase in active surface of cathode 336, with the result that an error signal is set up and amplified in amplifier 350. Not only is an error signal set up, but, due to the particular shift or location of the shadows, in this instance to the left as shown in Fig. 16, the signal will vary in sense as Well as in volume. The amplifier error signal will then be transmitted to the torque motor 360 which will react on the gyroscope through trunnion 305 to erect the gyroscope, and, in so doing, to cause the attitude gyro with its superposed member 368 to be restored to normal position. The torque motor, as previously indicated, is powered by generator 366 which is continuously driven by motor 310, the latter also serving as driving means for the shutter 3M mounted on the motor generator shaft.

From the showing in Fig. 16 it can be seen that when the shadow 309 moves to the right instead of to the left, as shown, a greater portion of the area of cathode 338 will be exposed to the light, while the major portion of cathode 336 will be masked. This condition will result in the inversion of the sense of the error signal from that obtained when the condition already described with respect to Fig. 16 is present. The effect of the angular deviation due to the acceleration, just described, is comparable to variations in the resistors 340 and 342 of the Wheatstone bridge circuit connected between the amplifier and the photoelectric cell. The current produced in the photoelectric cell will have a specic phase relation to shutter 3M. When the inclination varies opposite that indicated in Fig. 16 there will be a phase difference of 180 with respect to the reference phase generated by generator 366. The generator phase is caused to be displaced 90 from either of the tilt indications described above, so that when a signal of one phase is obtained from the erector 308, a rotating magnetic eld of one sign is obtained, whereas if the phase of the erector signal is reversed, the direction of rotation of the magnetic field is reversed. The erection may be readily eliminated during turns if desired by the introduction of a turn signal as sensed by some means responsive to acceleration forces, represented by box 344.

The device described provides a novel electrical gyro erector which has no electrical slip rings or connections on the gimbals of the gyro and no pendulous masses mounted on the gyro. As shown and described, the reference beam or stream 3|8 is a rising convection column, the position of which is compared with that of the post 308 on the gyro. When the housing 32.0 is tilted the erector herein should give no signal tending 12 to correct the gyro because the convection stream remains vertical, but if there is relative tilt of the gyroscope and stream the shadows will be displaced as previously described and a torque exerted on the gyroscope. Preferably, the torque applied to the gyroscope is relatively weak so that the resulting precession is slow as is customary in gyro verticals, so that the gyro does not respond to temporary displacement of the convection column, but only to a continued variation in relative tilt of the column and gyroscope.

It will now be appreciated that there has been provided a novel convection type gravity inclinometer and gyro erection control employing such inclinometer and characterized by an absence of pendulous mechanical parts, and consequent comparative freedom from conditions due to acceleration of pendulous parts during operation of aircraft With which they are associated.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. In a device of the character described, a closed envelope completely filled with a liquid, heating means providing a fixed, substantially point-source of heat at one end of said envelope for producing a rising, fine, columnar thermal convection stream in said liquid, means at the opposite end of said envelope and spaced from said one end having a thermally variable electrical characteristic, means associated with said last mentioned means forv determining a change in the electrical characteristics thereof, said liquid having a viscosity appreciably higher than that of water.

2. In an inclinometer, an envelope completely filled with a liquid, means providing a fixed substantially point-source of heat at one end of said envelope and situated on a central, normally vertical axis of said envelope for producing a rising, pencil-like, thermal convection stream in said liquid normally in coincidence with said axis, a plurality of thermally-variable electrical signal-producing means at the other end of said envelope and axially spaced from said one end, said signal-producing means being disposed Within said liquid in mutually spaced relation and in radially spaced relation to said axis, said lastmentioned means being adapted to provide a signal dependent upon the angle of inclination of said envelope relative to said convection stream.

3. An inclinometer comprising a fluid-tight vessel, a liquid medium filling the vessel, said liquid medium having a viscosity appreciably higher than that of water, heating means including a cone-shaped heating surface integral with the bottom of and projecting into the vessel at a central position thereof, said heating means producing by convection a fine rising stream of heated liquid Within the vessel, and thermal sensitive means including a plurality of thermocouples positioned adjacent the top of the vessel, said thermal sensitive means being responsive to the relative position of the upper portion of the rising stream of heated liquid.

4. An inclinometer comprising a fluid-tight vessel, a liquid medium filling the vessel, said liquid medium having a viscosity appreciably REFERENCES CITED The following references are of record in the le of this rpatent:

UNITED STATES PATENTS Number Name Date 1,132,617 Rector Mar. 23, 1915 1,192,911 Leeds Aug. 1, 1916 1,390,783 Hering Sept. 13, 1921 Number 15 Number 14 Name Date Antisell Nov. 17, 1925 Groh Apr. 15, 1930 Pfab Apr. 14, 1931 McBride Dec. 15, 1931 Kollsman Jan. 19, 1932 Buchholtz Dec. ll, 1934 Quereau Jan. 22, 1935 von Manteuiel et al. Mar. 30, 1943 Zworykin Apr. 20, 1948 Curry, Jr., et al. Dec. 2l, 1948 Webber Aug. 16, 1949 FOREIGN PATENTS Country Date Great Britain Oct. 18, 1917 Great Britain Feb. 13, 1919 Germany 1919 Germany Aug. 31, 1922 Germany Feb. 22, 1925 

